The Bacillus thuringiensis is a rod-shaped, Gram-positive, endospore-forming bacterium which is widely existing in various ecological environments. During the spore-forming phase, B, thuringiensis forms parasporal crystals consisting of Insecticidal Crystal Proteins (ICPs) which have specific toxicity against insects and specific biological activities to more than 500 species of insects in 10 orders belonging to the class Insecta, including Lepidoptera, Diptera, Coleoptera, Hymenoptera, Homoptera, etc, as well as to some harmful varieties in Protozoa, Nematomorpha, Platyhelminthes (Schnepf, H E., Crickmore, N., Rie, J. V., Lereclus, D., Baum, J., Feitelson, J., Zeigler, D. R. & Dean, D. H. 1998. Bacillus thuringiensis and its pesticidal crystal proteins. Microbiol Mol Biol Rev 62, 775-806).
Wildtype strains of B. thuringiensis typically have genes encoding insecticidal crystal proteins and each strain usually has multiple copies of said genes. Schnepf et al. cloned the first gene encoding insecticidal crystal protein in 1981 from B. thuringiensis subsp. kurstaki Strain HD1 and deduced the amino acid sequence of the first B. thuringiensis insecticidal crystal protein based on the DNA base sequence (Schnepf H E, Wong H C, Whiteley H R. The amino acid sequence of a crystal protein from Bacillus thuringiensis deduced from the DNA base sequence. J Biol. Chem. 1985 May 25; 260(10):6264-6272.). Afterwards, new genes encoding insecticidal crystal proteins have been actively pursued in connection with studies of B. thuringiensis. Many new genes encoding different insecticidal crystal proteins have been identified, cloned and sequenced. Therefore, in 1995, the B. thuringiensis Pesticidal Crystal Protein Nomenclature Committee was founded by scholars including Crickmore in the Annual Meeting of the Society for Invertebrate Pathology. In 1996, a new classification system for the B. thuringiensis insecticidal crystal proteins based on the homology of amino acid sequences was formally proposed, and nomenclature rules and the principle for classification were set, wherein it stipulates that: cry gene is an insecticidal gene from B. thuringiensis encoding parasporal crystal protein, or any gene that has obvious sequence similarity to a known cry gene; cyt gene is a gene encoding a parasporal crystal protein from B. thuringiensis that exhibits hemolytic activity, or any gene encoding a protein that has obvious sequence similarity to a known Cyt protein. They are classified in 4 ranks based on the homology of the amino acid sequence deduced from the full length gene. The boundaries between each rank represent approximately 95%, 78% and 45% sequence identity. The genes of the insecticidal crystal protein are classified into 4 ranks. By August, 2005, the number of genes of Bacillus thuringiensis insecticidal crystal proteins has reached 319, representing varieties from 48 types (Crickmore, N., D. R. Zeigler, J. Feitelson, E. Schnepf, J. Van Rie, D. Lereclus, J. Baum, and D. H. Dean. 1998. Revision of the nomenclature for the Bacillus thuringiensis pesticidal crystal proteins. Microbiol. Mol. Biol. Rev. 62:807-813; see for example the internet site at lifesci.sussex.ac.uk/home/Neil_Crickmore/Bt/index.html on the world wide web).
In the beginning, pesticides based on B. thuringiensis are produced with screened wildtype strains. With the advancement of molecular biology, people have gradually altered the wildtype strains by genetic engineering means. At the same time, people have been keeping on transforming genes of B. thuringiensis insecticidal crystal proteins into plants and have been producing transgenic plants that are resistant to agricultural pests.
However, with the development of B.t. pesticides and the increasing usage of these pesticides, resistance in targeted pests has been continuously discovered by the scientists. The scholars have extensively studied the resistance against B.t pesticides in targeted pests. Bacillus thuringiensis insecticidal crystal proteins have to go through the following process in order to give the insecticidal effects: the solubilization of the crystals and activation of the protoxin crystals, binding of the toxin fragments to receptors on the epithelial linings in the midgut, and the insertion into the membrane to create pores, wherein the activity spectrum and toxicity mainly depend on the recognition and interaction of the toxin fragments with the specific receptors on the epithelial linings in the midgut of the insects. Further, the development of resistance against B.t. pesticides in insects is closely related to the recognition and binding to the pesticide receptor. Therefore, cloning and application of new, especially novel genes of insecticidal crystal proteins have become the key to prevent and control the resistance against B.t pesticides in targeted pests and the core issue in the various insect control strategies. In recent years, searching and cloning novel genes of insecticidal crystal proteins have been the most active area in the study for B. thuringiensis. The significance of the present invention lies in this. In China, a new subspecies, YBT-978 strain, which is a subspecies of B. thuringiensis has been separated and characterized in 1996, which belongs to subspecies huazhongensis, serotype H40 (for the source of the strain, please refer to Dai J et al. 1996. Bacillus thuringiensis subsp. huazhongensis, serotype H40, isolated from soils in the People's Republic of China. Letters in Applied Microbiology. 22(1): 42-45). It is found the parasporal crystal proteins has a highly efficient insecticidal activity to insects including Plutella xylostella through extracting said parasporal crystal proteins and subjecting to bioassays.